Use buildah commit and bud in podman

Vendor in buildah and use as much of commit and bug as possible for podman
build and commit.

Resolves #586
Signed-off-by: baude <bbaude@redhat.com>

Closes: #681
Approved by: mheon

vendor/github.com/openshift/imagebuilder/signal/signal.go

@@ -0,0 +1,25 @@
+// Package signal provides helper functions for dealing with signals across
+// various operating systems.
+package signal
+
+import (
+	"fmt"
+	"strconv"
+	"strings"
+)
+
+// CheckSignal translates a string to a valid syscall signal.
+// It returns an error if the signal map doesn't include the given signal.
+func CheckSignal(rawSignal string) error {
+	s, err := strconv.Atoi(rawSignal)
+	if err == nil {
+		if s == 0 {
+			return fmt.Errorf("Invalid signal: %s", rawSignal)
+		}
+		return nil
+	}
+	if _, ok := SignalMap[strings.TrimPrefix(strings.ToUpper(rawSignal), "SIG")]; !ok {
+		return fmt.Errorf("Invalid signal: %s", rawSignal)
+	}
+	return nil
+}